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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >1,Ab Initio Analysis of the Structural Properties of ALkyL-Substituted Polyhedral Oligomeric Silsesquioxanes
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1,Ab Initio Analysis of the Structural Properties of ALkyL-Substituted Polyhedral Oligomeric Silsesquioxanes

机译：1，Ab从头算分析ALkyL取代的多面体寡聚倍半硅氧烷的结构性质

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摘要

Ab initio quantum mechanical calculations have been performed to establish the potentials for alkyl-substituted polyhedral oligomeric silsesquioxane (POSS) monomers R_xH_(8-x)(SiO_(1.5))_8. More specifically, we have examined the unsubstituted POSS (SiO_(1.5)H)_8 cage as well as linear and cyclic alkyl-substituted cages where one of the terminating hydrogen atoms is replaced by a hydrocarbon group, that is, R_1H_7(SiO_(1.5))8. The results for the minimum-energy configurations indicate that the presence of the linear hydrocarbon chains and cyclic intermediates have very little effect on the structure of the POSS cage. Although the POSS monomeric cage does influence the partial charges of the first few carbon atoms covalently bound to the POSS monomer, its effect on the structural properties of the alkyl chain is small. Differences arise, however, for cyclic alkyl substitutents bound to the POSS cage due to the repulsive interactions between the POSS cage and bulkier cyclic intermediates that result upon rotation of the Si-C-C-C dihedral angles. The interatomic potentials for these rotational, or torsional, terms need to be modified slightly in order to appropriately simulate sterically hindered substitutents on the cage. Our results suggest that combining an atomistic force field independently developed to describe silsesquioxanes with an independent atomistic model developed to describe hydrocarbon chains can be used in classical molecular simulation studies of most alkyl-silsesquioxanes. This avoids the need to develop specific force fields for each substituted POSS cage studied and opens up the possibility of using molecular simulation to probe the thermodynamic and structural properties of these unique nanoscale building blocks.
机译：从头进行了量子力学计算，以建立烷基取代的多面体低聚倍半硅氧烷（POSS）单体R_xH_（8-x）（SiO_（1.5））_ 8的电势。更具体地说，我们研究了未取代的POSS（SiO_（1.5）H）_8笼以及直链和环状烷基取代的笼，其中末端氢原子之一被烃基取代，即R_1H_7（SiO_（1.5 ））8。最小能量构型的结果表明，直链烃链和环状中间体的存在对POSS笼的结构影响很小。尽管POSS单体笼确实会影响与POSS单体共价键合的前几个碳原子的部分电荷，但其对烷基链结构特性的影响很小。但是，由于POSS笼与较大的环状中间体之间的排斥相互作用（由于Si-C-C-C二面角的旋转而导致）之间的排斥相互作用，导致与POSS笼结合的环状烷基取代基产生差异。这些旋转或扭转项的原子间电势需要稍作修改，以适当地模拟笼中的空间位阻取代基。我们的结果表明，将独立开发用于描述倍半硅氧烷的原子力场与开发用于描述烃链的独立原子模型相结合，可以用于大多数烷基倍半硅氧烷的经典分子模拟研究。这避免了为每个研究的取代的POSS笼子开发比力场的需要，并开辟了使用分子模拟来探究这些独特的纳米级构件的热力学和结构性质的可能性。

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